A nasal thermistor, a nasal pressure sensor, a chest-band sensor and the like are respiratory system monitors for detecting breathing (respiration), cough and yawn.
As for measuring, for example, the cough, various devices using a spiro-breathing flow meter (patent document 1), signals of the thyroid (patent document 2) and vibration of a catheter (patent document 3). These measuring devices and measuring methods are so complicated that the cough and the like cannot be easily measured in private homes or vehicles.
As simpler technologies, it is proposed to use a pattern of voice signals detected by a microphone (patent document 4) or voice signals and a sound pressure level detected by a microphone (patent document 5). The accuracy of detection is low due to noise, and it is difficult to specify the source of sound when there is a plurality of persons.
It is also proposed to use a camera image of a nose (patent document 6) or variation in a bed load (patent document 7). In case of using the image, the image is taken at a particular position imposing limitation on the position for taking a measurement. Besides, a person puts his or her hand to a mouth when coughing. Therefore, the hand becomes a blind which lowers the accuracy of detection. In case of using the bed load, the motion artifact such as body motion cannot be separated from the cough.
As a method of detecting yawn, further, it is proposed to use a camera image or voice (patent document 8). This method requires a complicated measuring device. It is also proposed to detect respiration conditions by analyzing pulse waves (patent documents 9 to 11).
[Patent document 1] JP-A-8-173403
[Patent document 2] JP-A-9-98964
[Patent document 3] JP-T-11-506380 (U.S. Pat. No. 5,899,927)
[Patent document 4] JP-A-7-376
[Patent document 5] JP-A-2003-38460
[Patent document 6] JP-A-8-257015 (U.S. Pat. No. 5,704,367)
[Patent document 7] JP-A-2003-552
[Patent document 8] JP-A-2005-199078
[Patent document 9] JP-A-2002-355227 (U.S. Pat. No. 6,669,632)
[Patent document 10] JP-A-2002-78690 (U.S. Pat. No. 6,856,829)
[Patent document 11] JP-A-2002-153432 (U.S. Pat. No. 6,856,829)